There are various touch screens for a computer which have different structures. A touch screen using photoelectric technology comprises an infrared touch screen using infrared emitting and receiving tubes and a camera touch screen using a camera to detect a location of a touch object. The principle of infrared touch screen is simple, but because a large number of infrared elements are used, its design, production, installation and debugging are complex, which leads to higher production costs. Moreover, because the infrared emitting tube would age, the life time of the infrared touch screen is not very long. Additionally, the infrared touch screen has a lower physical resolution. The technical principle and solution of the infrared touch screen can be found in U.S. Pat. Nos. 3,764,813, 3,860,754, 3,775,560 and 6,429,857 and a Chinese patent application No. 0012462.4. The touch screen with an image sensor (camera) has advantages of high hardware integration, simple structure and lower production costs, but in the prior art, at least two cameras can constitute an image detecting system for a touch screen. Therefore, two sets of micro-computer systems for image processing are necessary, which causes high hardware cost. The work principle and technical solution of such technology can be found in a German patent No. DE20016024549.